As there are WiFi issues from time it would be very useful if there was an option in the App to toggle connectivity between WiFi and Bluetooth.
Specifically, my kitchen and router are on a different floor, my control with app through WiFi connection is very unstable and sometimes even fails completely (which is a pain if you are in the middle of cooking). The only stable connection is Bluetooth
However, I’d like to use the WiFi features from time to time, remote control outside the house, control from the bottom floor and Amazon Echo features.
To toggle between the two modes today means resetting to default and re connect, it’s too much…
So, the problem isn’t your phone losing connectivity - it’s that the APC has a weak wifi radio…and often can’t make that data connection to your WAP/router.
(your phone doesn’t need to have a wifi connection to connect to the APC - it just needs a data connection - cellular works).
Me, I’d get a wifi range extender and put it on the same floor as your kitchen…or, hell, move the APC and your vessel to the floor where the router is. 
(I actually normally put mine in my spare bedroom) But, I also have a vessel with a sealed cover, so not a lot of odours or steam coming from it.